The VIR Spectrometer

The Dawn spectrometer (VIR) is a hyperspectral spectrometer with imaging capability. The design fully accomplishes Dawn’s scientific and measurement objectives. Determination of the mineral composition of surface materials in their geologic context is a primary Dawn objective. The nature of the solid compounds of the asteroid (silicates, oxides, salts, organics and ices) can be identified by visual and infrared spectroscopy using high spatial resolution imaging to map the heterogeneity of asteroid surfaces and high spectral resolution spectroscopy to determine the composition unambiguously. The VIR Spectrometer—covering the range from the near UV (0.25 μm) to the near IR (5.0 μm) and having moderate to high spectral resolution and imaging capabilities—is the appropriate instrument for the determination of the asteroid global and local properties. VIR combines two data channels in one compact instrument. The visible channel covers 0.25–1.05 μm and the infrared channel covers 1–5.0 μm. VIR is inherited from the VIRTIS mapping spectrometer (Coradini et al. in Planet. Space Sci. 46:1291–1304, 1998; Reininger et al. in Proc. SPIE 2819:66–77, 1996) on board the ESA Rosetta mission. It will be operated for more than 2 years and spend more than 10 years in space.     

How Important are the Equations of Motion in a Chaotic System?

We inquire whether some important features might be lost in studying the gravitational n–body problem because chaos makes it impossible to follow exact phase trajectories. We test this by comparing deliberately crude `integrations' with published results from more precise methods. A general tendency found with high-quality integrations is that a central singularity forms at finite time. The time until that singularity forms is fairly reproducible for systems started from a more or less standard form. We find the same tendency with crude methods, although the time to reach that singularity from the usual initial conditions is less accurately reproduced with cruder methods.     

New ATC requirements phasing in preparation for the C-17 GATM/NAV safety functions to meet civil requirements

For the next 10 years new worldwide communication, navigation, and surveillance (CNS) requirements are being incrementally imposed upon commercial aircraft avionics, and upon the Air Traffic Control community, by the Aviation Administrations of most nations, including the FAA and the JAA. These requirements are the result of a decade of study by the United Nations' International Civil Aviation Organization (ICAO) to improve aviation safety and efficiency. In 2001, the USAF mandated compliance to the CNS requirements for its military aircraft, which is called Navigation Safety/Global Air Traffic Management (NS/GATM) by the USAF. By complying with these requirements, the C-17 will maintain its ability to fly internationally without CNS restrictions, such as requiring special handling. The Phase I study reported herein is the first phase of a three-phase study effort that will result in the C-17 achieving NS/GATM compliance for a specific set of NS/CNS requirements.     

Software approach to access UWB interference on GPS receivers

Ever since the FCC approved the use of UWB devices in commercial and federal bands, various agencies whose operations and/or products rely on the integrity of signals within certain "restricted" radio frequency bands have voiced concerns over the potential impact of the UWB interference. GPS signals are among these "restricted" bands. Several groups in the GPS community have conducted experimental studies concerning the impact of UWB interference on the performance of various grades of commercial and aviation GPS receivers. In this paper, we present a software approach to simulate and evaluate UWB interference on GPS receivers. The software approach provides greater flexibility in the design of testing scenarios, such as the inclusion of a large number of aggregated UWB devices, the generation of new UWB signals and modulation schemes, and the possibility of extending the study to new GPS signals. The paper discusses a general framework for developing algorithms to evaluate UWB and GPS interference under a wide variety of hardware and software conditions. This framework consists of three classes of components: input, processing, and analysis. The input components are responsible for the generation of UWB signal waveforms and modulation schemes, and GPS signals. The processing components include a simulated model of GPS RF front end and software implementation of GPS processing blocks, such as acquisition, tracking, and post-processing. The analysis components focus on the study of specific receiver processing component outputs. Both real and simulated UWB signals can be used in the study. The real UWB signals are primarily used to validate the simulation procedure, whereas the simulated UWB signals are used to allow the immediate incorporation of new UWB waveforms and modulations in the evaluations. This paper presents details of the software components developed and the preliminary results achieved     

Physics of Magnetospheric Variability

Many widely used methods for describing and understanding the magnetosphere are based on balance conditions for quasi-static equilibrium (this is particularly true of the classical theory of magnetosphere/ionosphere coupling, which in addition presupposes the equilibrium to be stable); they may therefore be of limited applicability for dealing with time-variable phenomena as well as for determining cause-effect relations. The large-scale variability of the magnetosphere can be produced both by changing external (solar-wind) conditions and by non-equilibrium internal dynamics. Its developments are governed by the basic equations of physics, especially Maxwell’s equations combined with the unique constraints of large-scale plasma; the requirement of charge quasi-neutrality constrains the electric field to be determined by plasma dynamics (generalized Ohm’s law) and the electric current to match the existing curl of the magnetic field. The structure and dynamics of the ionosphere/magnetosphere/solar-wind system can then be described in terms of three interrelated processes: (1) stress equilibrium and disequilibrium, (2) magnetic flux transport, (3) energy conversion and dissipation. This provides a framework for a unified formulation of settled as well as of controversial issues concerning, e.g., magnetospheric substorms and magnetic storms.     

节能环保的米勒Dynasty 700型逆变氩弧焊机

Dynasty 700将先进的逆变技术的优势和高端交直流氩弧焊电源的特点相结合,以紧凑的结构提供卓越的电弧性能。该产品输出范围大,拥有高达500A/40V,100%暂载率,兼容大电流的铜焊接和铝合金焊接的自动工艺。Auto-Line为米勒专利的电     

High-Precision Laboratory Measurements Supporting Retrieval of Water Vapor,Gaseous Ammonia,and Aqueous Ammonia Clouds with the Juno Microwave Radiometer (MWR)

The NASA Juno mission includes a six-channel microwave radiometer system (MWR) operating in the 1.3–50 cm wavelength range in order to retrieve abundances of ammonia and water vapor from the microwave signature of Jupiter (see Janssen et al. 2016). In order to plan observations and accurately interpret data from such observations, over 6000 laboratory measurements of the microwave absorption properties of gaseous ammonia, water vapor, and aqueous ammonia solution have been conducted under simulated Jovian conditions using new laboratory systems capable of high-precision measurement under the extreme conditions of the deep atmosphere of Jupiter (up to 100 bars pressure and 505 K temperature). This is one of the most extensive laboratory measurement campaigns ever conducted in support of a microwave remote sensing instrument. New, more precise models for the microwave absorption from these constituents have and are being developed from these measurements. Application of these absorption properties to radiative transfer models for the six wavelengths involved will provide a valuable planning tool for observations, and will also make possible accurate retrievals of the abundance of these constituents during and after observations are conducted.     

Radar-Derived Properties of the InSight Landing Site in Western Elysium Planitia on Mars

We carried out an assessment of surface and subsurface properties based on radar observations of the region in western Elysium Planitia selected as the landing site for the InSight mission. Using observations from Arecibo Observatory and from the Mars Reconnaissance Orbiter’s Shallow Radar (SHARAD), we examined the near-surface properties of the landing site, including characterization of reflectivity, near-surface roughness, and layering. In the Arecibo data (12.6-cm wavelength), we found a radar-reflective surface with no unusual properties that would cause problems for the InSight radar altimeter (7-cm wavelength). In addition, the moderately low backscatter strength is indicative of a relatively smooth surface at \({\sim} 10\mbox{-cm}\) scales that is composed of load-bearing materials and should not present a hazard for landing safety. For roughness at 10–100 m scales derived from SHARAD data, we find relatively low values in a narrow distribution, similar to those found at the Phoenix and Opportunity landing sites. The power of returns at InSight is similar to that at Phoenix and thus suggestive of near-surface layering, consistent with a layer of regolith over bedrock (e.g., lava flows) that is largely too shallow (\({<}10\mbox{--}20~\mbox{m}\)) for SHARAD to discern distinct reflectors. However, an isolated area outside of the ellipse chosen in 2015 for InSight’s landing shows faint returns that may represent such a contact at depths of \({\sim} 20\mbox{--}43~\mbox{m}\).     

Estimations of the Seismic Pressure Noise on Mars Determined from Large Eddy Simulations and Demonstration of Pressure Decorrelation Techniques for the Insight Mission

The atmospheric pressure fluctuations on Mars induce an elastic response in the ground that creates a ground tilt, detectable as a seismic signal on the InSight seismometer SEIS. The seismic pressure noise is modeled using Large Eddy Simulations (LES) of the wind and surface pressure at the InSight landing site and a Green’s function ground deformation approach that is subsequently validated via a detailed comparison with two other methods: a spectral approach, and an approach based on Sorrells’ theory (Sorrells, Geophys. J. Int. 26:71–82, 1971; Sorrells et al., Nat. Phys. Sci. 229:14–16, 1971). The horizontal accelerations as a result of the ground tilt due to the LES turbulence-induced pressure fluctuations are found to be typically \(\sim 2 \mbox{--} 40~\mbox{nm}/\mbox{s}^{2}\) in amplitude, whereas the direct horizontal acceleration is two orders of magnitude smaller and is thus negligible in comparison. The vertical accelerations are found to be \(\sim 0.1\mbox{--}6~\mbox{nm}/\mbox{s}^{2}\) in amplitude. These are expected to be worst-case estimates for the seismic noise as we use a half-space approximation; the presence at some (shallow) depth of a harder layer would significantly reduce quasi-static displacement and tilt effects.We show that under calm conditions, a single-pressure measurement is representative of the large-scale pressure field (to a distance of several kilometers), particularly in the prevailing wind direction. However, during windy conditions, small-scale turbulence results in a reduced correlation between the pressure signals, and the single-pressure measurement becomes less representative of the pressure field. The correlation between the seismic signal and the pressure signal is found to be higher for the windiest period because the seismic pressure noise reflects the atmospheric structure close to the seismometer.In the same way that we reduce the atmospheric seismic signal by making use of a pressure sensor that is part of the InSight Auxiliary Payload Sensor Suite, we also the use the synthetic noise data obtained from the LES pressure field to demonstrate a decorrelation strategy. We show that our decorrelation approach is efficient, resulting in a reduction by a factor of \(\sim 5\) in the observed horizontal tilt noise (in the wind direction) and the vertical noise. This technique can, therefore, be used to remove the pressure signal from the seismic data obtained on Mars during the InSight mission.